It has been said that “water is the oil of the 21st century” because of its huge demand and finite supply. Although it is estimated that greater than 75% of the earth's surface is covered by water, only a very small fraction of that water is drinkable or usable without treatment. Over 96% of water is ocean, seas and bays. Of fresh water, nearly 70% is trapped in ice caps, glaciers and permanent snow. (See, www.earthobservatory.nasa.gov). Salt water, which represents the vast majority of water, requires an expensive and energy intense desalination process before it is can be used for drinking.
The U.S. has more than 97,000 water treatment facilities. The projected annual growth rate for water treatment is 5%-8% over the next decade. Furthermore, the Environmental Protection Agency (EPA) has projected that this increase will come primarily from population growth and urban expansion. Because of increased demand, there is recognized a need to upgrade equipment used in the water treatment industry, particularly the wastewater treatment industry. Equipment installed under the Clean Water Act of 1972 is currently approaching the end of its projected lifecycle. In addition, the water treatment standards mandated by the EPA do, from time to time, become more stringent.
In addition to a limited access to fresh water, we face an increasing dilemma related to energy. “By many measures, the world's energy system”—including electricity—“is not keeping pace with the goals of sustainable development.” In an attempt to meet these demands, “ . . . the established system generates harmful particulate and chemical pollutants that threaten the health and the environment of the world's people.” See, the Program on Energy and Sustainable Development at Stanford University, January 2006. With respect to the United States, it is well known that our own power systems are continually faced with an ever-increasing demand for more electricity. We are also confronted with the ongoing need to produce additional electricity without increasing the demand for more water and without further contributing to emissions.
Thus, the issues pertaining to water as a resource and energy reserves are intertwined on many levels. An April 2005 Lawrence Berkeley National Laboratory Study estimated the electricity potential from methane produced by the anaerobic digestion of wastewater biosolids, from Industrial, Agriculture, and Municipal facilities. See E. O. Lawrence Berkeley National Laboratory Study, April 2005, LBNL-57451. The result demonstrated that, notwithstanding energy requirements to process water, the processing of water can itself be a source of energy.
Traditionally, water treatment facilities are constructed to take in wastewater as influent 102 and process it through a variety of screenings and treatments, as illustrated in FIG. 1, prior to the releasing the effluent 120 to the ocean, bay, river or lake 122. Solids and grit are removed via a bar screen 104 and a grit screen 106 and sent to a landfill 112. Wastewater that passes through the bar screen 104 and the grit screen 106 is subjected to primary treatment 109 in a large sedimentation lagoon or tank 114. The sedimentation tank 114 enables particle settling or sedimentation. The sedimentation tank has an influent which travels in at a flow rate, Q, the influent travels through the tank to an opposing end where it exits as effluent. During the process of traveling from the inlet (as influent) to the outlet (as effluent), particles settle out in a settling zone to form a sludge at the bottom of the tank. A variety of techniques can be employed to remove the particles from the sedimentation tank that would be known to those skilled in the art.
From the sedimentation tank 114 the sediment flows into a stabilization lagoon or tank 116 before dewatering 118 and reuse or disposal 112′. The effluent flows from the sedimentation tank 114 to an aeration tank 117 where it is brought into contact with air prior to transferring the effluent to a second sedimentation lagoon 114′ as part of a secondary treatment process 115. After secondary treatment 115 in the aeration tank 117 and sedimentation lagoon 114′, the effluent can be processed with a final disinfectant step 121 by placing into a chlorination basin 119 prior to emitting the final effluent 120 into the ocean, bay, river or lake 122. The sedimentation can be placed into a stabilization lagoon 116′ before dewatering 118, reuse or disposal 112′.
Conventional treatment technologies include, for example, a pumped diffusion flash mixer for chemical addition, flocculation basin, sedimentation basin and granular medium filter. The residuals from the wastewater treatment plant are returned to the source or stored in ponds. For example in arid locations, drying ponds are sometimes used. More often, mechanical processing is employed in conjunction with the residuals to reduce the volume of the residuals. Yet another treatment mechanism that can be used after primary treatment is provided by G.E. Water & Processing Technologies and includes ZeeWeed based membrane bioreactor (MBR). The ZeeWeed MBR is a basic production train that consists of a biological reactor, membrane basin, permeate pump, air blowers and automated control equipment. The trains are simply expanded to meet capacity requirements as needed. Membrane bioreactor systems offer a significantly smaller footprint and simplified operation than the comparable conventional activated sludge systems shown in FIG. 1. However, the systems are still quite large. (See, http://www.zenon.com/markets/wastewater/).
Currently there are several important issues facing the design of current wastewater treatment facilities for which there has been an insufficient solution. First, most wastewater treatment facilities consume a significant amount of energy during operation. Second, wastewater treatment facilities typically require a substantial amount of land. Third, wastewater treatment facilities often emit an unpleasant odor which can make them undesirable to place strategically in an urban setting, notwithstanding the space requirements. Fourth, wastewater treatment facilities present a potential security risk because the facilities are part of a critical infrastructure that must be protected to ensure an adequate supply of water.